1. Field of the Invention
The present invention relates to a monopulse radar system, further detailedly relates to a monopulse radar system that radiates a radio wave, receives a reflected radio wave from a body where the radio wave is detected with plural receiving antennas and detects the direction of the detected body depending upon difference in amplitude or a phase between signals received by the plural receiving antennas and particularly relates to a monopulse radar system suitable for a radar used for a car and mounted on a mobile body such as a vehicle.
2. Description of the Related Art
Heretofore, a radar system used for a car and mounted on a mobile body such as a vehicle for detecting the velocity and the position of a detected body such as the mobile body and an obstacle is known. For a radar system used for a car, a radar system used for a car in which antenna beam width is switched from wide one to narrow one and vice versa corresponding to a detected body and the velocity and the position of the detected body are precisely detected and a radar system used for a car in which the direction of the detected body can be detected are developed.
For a document related to the former, for example, Japanese published unexamined patent application No. Hei 2-287181, xe2x80x9cRADAR SYSTEM USED FOR CARxe2x80x9d and Japanese published unexamined patent application No. 2000-258524 can be given.
For the latter primary radar system for detecting the direction of a detected body, a mechanical scanning system of mechanically turning an antenna by a motor, a beam switching system of switching plural antennas different in the orientation of a beam (for example, disclosed in Japanese published unexamined patent application No. Hei 8-334557) and a monopulse system (for example, described on pages 8 to 19 of xe2x80x9cMonopulse Principles and Techniquesxe2x80x9d published by ArtechHouse and written by Samuel M. Sherman) can be given.
According to the monopulse system, as shown in FIG. 10, reflected waves 29 from an obstacle 28 are received by two receiving antennas 30 and a sum signal p and a difference signal q are generated in a hybrid circuit 8. Relation between the relative electric power of the generated sum signal p and the generated difference signal q and an azimuth is as shown in FIG. 11 and relation between the ratio t of the sum signal p and the difference signal q and an azimuth is as shown in FIG. 12. As shown in FIG. 12, as the ratio t of the sum signal p and the difference signal q is a monotone decreasing function in relation to an azimuth, the azimuth of a detected body can be uniquely determined based upon the ratio t of the sum signal and the difference signal. High-resolution angle detection can be also performed in a wide range by increasing the number of receiving antennas.
Recently, it is demanded for a radar system used for a car that the direction of a detected body is precisely detected at the same time as the velocity and the position of the detected body are precisely detected. Further, as the radar system is used for a car, it is demanded that the radar system has simple configuration, is compact and the manufacturing cost is low. The above-mentioned conventional type monopulse system is excellent in azimuth resolution, compared with another system and relative miniaturization is possible. However, antenna beam width is required to be widened to enlarge a detectable directional range, a detectable distance range is narrowed and azimuth resolution is also deteriorated. To enlarge a detectable azimuth without deteriorating detectable distance and azimuth resolution, an antenna that generates a wide angle beam and an antenna that generates a narrow angle beam are required to be provided and to be switched, and there is a problem that the system is large-sized and the cost is increased.
Therefore, the invention is made to solve the problem and it is the object to provide a low-cost, compact and light monopulse radar system wherein the monopulse system is improved, a detectable range of the position (distance between an antenna and a detected body) of the detected body and relative velocity can be switched to a sharp angle/long distance or a wide angle/short distance and simultaneously the precise azimuth of an obstacle can be detected in the range.
To achieve the object, in the monopulse radar system according to the invention, at least one of a transmitting antenna and a receiving antenna is formed by an array antenna composed of plural antenna elements, the plural antenna elements are divided into plural groups, an antenna switch to switch the plural groups is provided and a switch control device to control the opening and closing of the antenna switch is provided to switch an antenna beam of at least the transmitting or receiving antenna to a sharp angle/long distance or a wide angle/short distance.
In the invention, a detectable range of distance up to a mobile obstacle and relative velocity can be switched to a sharp angle/long distance or a wide angle/short distance by switching the antenna switch of the array antenna, simultaneously the accurate azimuth of the obstacle can be detected in the detectable range and in case antenna beams cover a sharp angle and long distance, higher-accuracy azimuth detection is enabled. As a detection range is switched by connection and disconnection in units of an antenna element, multiple independent array antennas the orientation of which is determined are not required and the simple antenna switch is provided to the array antenna, the low-cost, compact and light system can be realized.
Beam switching technique in which the velocity of a detected body such as a mobile body and an obstacle and distance up to it are detected in a state of suitable beam width by switching beam width according to distance up to the detected body (disclosed in for example, Japanese published unexamined patent application No. Hei 2-287181, xe2x80x9cRADAR SYSTEM USED FOR CARxe2x80x9d) is known, however, according to the beam switching technique, the azimuth of a detected body cannot be detected. In the invention, it is first found and realized by combining beam switching technique and a monopulse radar system that in case antenna beams cover a sharp angle and long distance, higher-accuracy azimuth detection which is not acquired in each of the beam switching technique and the monopulse radar system is enabled, utilizing the advantages of a monopulse radar.
As a monopulse radar system according to the invention is provided with the antenna switch for switching beams from the transmitting array antenna and the receiving array antenna respectively composed of plural antenna elements to a sharp angle/long distance or a wide angle/short distance, a detectable range of distance up to a mobile obstacle and relative velocity can be switched to a sharp angle/long distance or a wide angle/short distance, as a monopulse system is used, the accurate azimuth of the obstacle can be detected in the range, in case antenna beams cover a sharp angle and long distance, higher-accuracy azimuth detection is enabled, the detectable range is switched by connection and disconnection in units of an antenna element and as plural array antennas are not required, the low-cost, compact and light monopulse radar system can be realized.
This and other advantages of the present invention will become apparent to those skilled in the art on reading and understanding the following detailed description with reference to the accompanying figures.